Speaking two languages may keep the mind sharp longer than knowing only a single language, even in those who can't read.

Scientists reviewed the records of 391 bilingual and 257 monolingual patients diagnosed with dementia between 2006 and 2012 at a clinic in Hyderabad, India. Patients who spoke two languages developed the first signs of dementia an average of 4.5 years later than people who only spoke one language.